A known method for automatically loading moved trays is, e.g. loading a tray from above. The items may be loaded onto the tray top-down at an acute angle and in free fall. Owing to the drop height, the items are burdened with a load and, thus, the items might tip over. Furthermore, the angle of the discharge conveyor relative to the tray depends on the lengths of the items. Accordingly, it may be difficult to load items with large varying lengths by means of one and the same discharge conveyor.
The method and the system according to DE 10 2008 055 704 A1 relates to the unloading of trays loaded with items. To this end, the tray consists of a frame with circumferential raised rim and of a floor having at least one opening. Within said rim, a transport plate is provided on the floor. For unloading the tray, the frame will be lowered until the upper surface of the transport plate is on the same level with the circumferential raised rim so that the items can be pushed off the transport plate. To lower the tray frame easily, a lowering device comprising supporting elements which grasp through said at least one opening from below, which are movable in the direction of transportation, may comprise a second conveyor subsequent to a first delivery conveyor, the level thereof being lowered with regard to said delivery conveyor.
The transport plate serving as a support can be guided in a flexibly linked manner with the frame of the tray via pins or guides so as to prevent, due to such linkage, any horizontal movement/shift of the plate but to enable a vertical movement thereof perpendicular to the floor of the frame.
The groups of supporting elements may be preceded by stop elements for aligning the positions of the trays. The tray comes from the first delivery conveyor and hits a corresponding stop element in the transfer zone, so that said at least one opening of the respective tray or the frame thereof is in alignment with the subsequently following group of supporting elements.
DE 41 02 654 C2 describes a loading and unloading device for trough-shaped trays, the floors thereof being provided with slots. By means of a clock-controlled circulating chain, the loading and the unloading stations are linked to supporting webs which may be passed through slots of the tray floor and project beyond the side walls of the trays. Conveyor zones connect at both ends of said circulating chain, are driven synchronously with the circulating chain and extend laterally along the circulating chain with said supporting webs over a transfer zone where a vertical transfer movement takes place.
Due to the vertical transfer movement, the supporting webs are being moved upwards through the slots of the tray floor while the trays are entering the chain conveyor, thus lifting the items to be conveyed to a height beyond the rim edges of the trays so that they can be removed towards the sides.
In the loading station, the items are placed onto the supporting webs which will then be moved out again downwards through the tray slots so that the items are placed onto the trays.
Loading and unloading of the trays can be done while the chain is circulating by pushing the items, during loading, from the supporting webs towards the side or by pushing them, in the loading station, from the side onto the chain webs.
Furthermore, the chain circulation may repeatedly be stopped in a clock-controlled manner in the unloading station and, correspondingly, in the loading station in order to either remove or place the items from or onto the supporting webs which might be done, for instance, by means of a removing or positioning rake.
While the supporting webs are either entering or leaving, the vertical movement is also accompanied by a horizontal movement of the supports, i.e. turn in or turn out, which leads, with increasing web height and smaller radius of the chain conveyor guide in the entering or leaving zone, to increasingly larger tray slots and large slot or supporting web distances. An increasing distance between the supporting webs leads to instability while placing and transporting the items, especially in case of short items, and, beyond, to a more complex push-on and push-off process for the items, as a smaller number of supporting webs may result in a reduced supporting area and, thus, to increased friction and to an increased wear of the packing of the items. Likewise, the dynamics occurring during loading and unloading can be reduced and a continuous transport of the trays during loading and unloading even be prevented which will imply that the trays may have to be stopped.
Patent specification DE 41 43 282 C1 discloses the use of trays having floors provided with slot-shaped openings into which profile bodies of dimensions corresponding to said openings can either be vertically moved in or moved out from below.
Starting from the floor of the tray to the rim of the tray, the profile bodies form an upwards inclined transport surface, the angle between floor and transport surface being selected such that pushing-off of the item can be safely ensured. The profile bodies are brought in at one side by means of a lifting device to avoid that not the whole item on the tray will be lifted by said profile bodies but that only a partial lifting of the item takes place.
Aligning the tray to the transfer position is done via centering elements in the form of studs so as to enable a trouble-free entering of said profile bodies.